This application claims the priority benefit of Japanese application serial no. 2001-287619, filed Sep. 20, 2001.
1. Field of the Invention
The present invention is related to a weld quality evaluation apparatus for consumable electrode gas shielded arc welding.
2. Background Art
In the past, judgments on the acceptability of weld quality in consumable electrode gas shielded arc welding (hereinafter xe2x80x9carc weldingxe2x80x9d), were made by inspectors performing after-the-fact external visual inspections to check the uniformity and shape of the bead, and the amount of spatter deposited. In this method, precise pass/fail assessments of weld quality were difficult to achieve due to reliance on qualitative assessments made by different individuals.
A proposed solution to this problem was described in Publication of Unexamined [Japanese] Patent Application No. H10-137938 (hereinafter, xe2x80x9cfirst background art referencexe2x80x9d). This proposal uses an arc welding monitoring system in which weld quality acceptability is assessed indirectly from the rate at which the consumable electrode (welding wire) is fed out, and the amount of welding wire supplied.
Another solution was proposed in Unexamined [Japanese] Patent Application No. H9-57442 (hereinafter, xe2x80x9csecond background art referencexe2x80x9d). This reference proposed an arc welding monitoring system in which a number of quantitative characteristics related to arc welding quality are monitored by separate sensors to determine whether the arc welding is being performed according to a prescribed set of conditions.
A problem with the technology of the first reference (JP H10-137938), however, is that in this method it is difficult, based solely on welding wire feed rate and the amount of wire supplied, to assess factors such as
(1) whether the optimum amount of molten welding wire metal was deposited;
(2) whether enough welding wire metal had penetrated into the workpiece material to ensure adequate bonding strength after welding; and
(3) how much of the spatter generated during welding was wasteful.
Also, in the solution proposed in the second reference (JP H9-57442), a number of quantitative characteristics related to arc welding quality are monitored by separate sensors for sensing welding voltage/current, remaining gas pressure, remaining wire, etc., and welding quality is assessed based on the results of this sensing. Therefore, in this method, although it is possible to assess trends associated with continuous variations in remaining shielding gas pressure, remaining wire, etc., it is difficult to assess welding quality when there are instantaneous changes occurring during welding due to arc interruption phenomena. This can lead to erroneous assessments of arc welding quality.
The present invention was devised with the above problem in mind, and it is therefore an object thereof to provide an arc welding quality evaluation apparatus that can make precise welding quality pass/fail decisions, and that does not make erroneous welding quality assessments. The present invention accomplishes the above object through the technical means described below.
That is, to accomplish the above object, an arc welding quality evaluation apparatus according to a first aspect of the present invention is characterized in that in consumable electrode gas-shielded arc welding, wherein a welding voltage is applied between a welding wire and a workpiece to be welded, molten metal droplets from the welding wire are transferred to the workpiece, and that portion of the wire consumed by the transfer of droplets is replenished, for performing continuous arc welding, it comprises a heat input detection means for detecting heat input applied to the workpiece, from the welding voltage applied thereto and welding current supplied thereto; a welding time detection means for detecting workpiece welding time: a spatter weight detection means for detecting the weight of spatter produced during the workpiece welding time; a heat compensation means for compensating for heat loss due to spattering during the workpiece welding time; an effective heat input computation means for computing effective heat input based on detected values of the heat input detection means and welding time detection means, and a heat compensation value of the heat compensation means; and a weld quality assessment means for assessing weld quality acceptability based on the degree of separation of an output of the effective heat input computation means from a reference standard value.
This first aspect of the present invention is based on the fact that weld quality assessment accuracy is closely related to the effective heat input (heat input applied to the workpiece, compensated for heat loss due to spattering). The effective heat input value found to exist during optimum welding is set in advance as the reference standard value. Values output from the effective heat input computation means are then compared to this reference standard value, and welding quality pass/fail decisions are made based on the degree of separation of the values output by the effective heat input computation means from the reference standard value.
Also, a second aspect of the present invention is characterized in that, in a consumable electrode gas shielded arc welding system, it comprises a supplied wire weight detection means for detecting the weight of welding wire supplied, a spatter weight detection means for detecting the weight of spatter produced during the workpiece welding time; a weld metal deposition efficiency computation means for computing efficiency of deposition of welding wire metal on the workpiece, based on values detected by the supplied wire weight detection means and the spatter weight detection means; and a weld quality assessment means for comparing an output value of the weld metal deposition efficiency computation means with a reference standard value, and assessing weld quality acceptability based on the degree of separation of the computation means output value from the reference standard value.
This second aspect of the present invention is based on the fact that weld quality assessment accuracy is closely related to weld metal deposition efficiency (the weight of the welding wire supplied minus the weight of the spatter, all divided by the weight of the wire supplied). The weld metal deposition efficiency found to exist during optimum welding is set in advance as the reference standard value. Values output by the deposition efficiency computation means are then compared to this reference standard value, and welding quality pass/fail decisions are made based on the degree of separation of the values output by the deposition efficiency computation means from the reference standard value.
A third aspect of the present invention is characterized in that, in a consumable electrode gas-shielded arc welding system, it comprises a supplied wire weight detection means for detecting the weight of welding wire supplied; a spatter weight detection means for detecting the weight of spatter produced during the workpiece welding time; a deposited metal weight computation means for computing the weight of welding wire metal deposited on the workpiece, based on values detected by the supplied wire weight detection means and spatter weight detection means; and a welding quality assessment means for comparing an output value of the deposited metal weight computation means with a reference standard value, and assessing weld quality acceptability based on the degree of separation of the output value from the reference standard value.
This third aspect of the present invention is based on the fact that weld quality assessment accuracy is closely related to the weight of the deposited welding wire metal (the weight of the supplied wire minus the weight of the spatter). The weight of the deposited weld metal found to exist during optimum welding is set in advance as the reference standard value. The value output by the deposited metal weight computation means is then compared to this reference standard value, and welding quality pass/fail decisions are made based on the degree of separation of the values output by the deposited metal weight computation means from the reference standard value.
A fourth aspect of the present invention is characterized in that it comprises a welding quality assessment means that computes a molten metal cross-sectional area of a workpiece, using a first conversion diagram for converting an output value of an effective heat input computation means according to the above first aspect to a workpiece molten cross-sectional area, compares the molten metal cross-sectional area to a reference standard value, and assesses weld quality acceptability based on the degree of separation of the molten metal cross-sectional area from the reference standard value.
This fourth aspect of the present invention is based on the fact that effective heat input is essentially directly proportional to the molten metal cross-sectional area of the workpiece. Also, the molten metal cross-sectional area and depth of weld penetration are closely related to weld quality acceptability. Therefore, the effective heat input corresponding to the molten metal cross-sectional area found to exist during optimum welding is set in advance as the reference standard value. Values output by the effective heat input computation means are compared to this reference standard value, and welding quality pass/fail decisions are made based on the degree of separation of the computed values from the reference standard value.
A fifth aspect of the present invention is characterized in that it comprises a welding quality assessment means that computes a deposited metal cross-sectional area of a workpiece, using a second conversion diagram that converts an output value of a deposited metal weight computation means according to the above third aspect to a deposited metal cross-sectional area, compares the deposited metal cross-sectional area to a reference standard value, and assesses weld quality acceptability based on the degree of separation of the deposited metal cross-sectional area from the reference standard value.
This fifth aspect of the present invention is based on the fact that the weight of the deposited metal is essentially directly proportional to the deposited metal cross-sectional area of the workpiece. The acceptability of welding quality is closely related to the deposited metal cross-sectional area. Therefore, the deposited weight corresponding to the deposited metal cross-sectional area found to exist during optimum welding is set in advance as the reference standard value. Values output by the deposited metal weight computation means are compared to this reference standard value, and welding quality pass/fail decisions are made based on the degree of separation of this computation means output from the reference standard value.
A sixth aspect of the present invention is characterized in that it comprises a welding quality assessment means that computes an effective cross-sectional area by subtracting the deposited metal cross-sectional area according to the above fifth aspect from the molten metal cross-sectional area according to the above fourth aspect, compares the effective cross-sectional area to a reference standard value, and assesses weld quality acceptability based on the degree of separation of the effective cross-sectional area from the reference standard value.
A seventh aspect of the present invention is characterized in that, in an arc welding quality evaluation apparatus according to any one of the first through sixth aspects of the invention, it comprises a weld quality assessment means wherein effective heat input, deposited metal weight, molten metal cross-sectional area, deposited metal cross-sectional area, and effective cross-sectional area, as in the first through sixth aspects, are computed as average values over the welding time, each average value is compared to a reference standard value set to the respective average value during optimum welding conditions, and weld quality acceptability is assessed based on the degree of separation of the average value from the reference standard value.
The cross-sectional area of the weld penetration depth and leg length (as indicated in the cross-hatched portions of FIG. 7) is the best indication of welding quality. The cross-sectional area of this portion is designated as the xe2x80x9ceffective cross-sectional area.xe2x80x9d This effective cross-sectional area (the cross-sectional area of the penetration of the weld into the workpiece), is the cross-sectional area of the molten metal minus the cross-sectional area of the deposited metal. From a plot of molten metal cross-sectional area vs. effective heat input data obtained in experiments in which effective heat input per unit time is varied over a broad range, a first conversion diagram for converting effective heat input to workpiece molten metal cross-sectional area can be generated. Similarly, from a plot of deposited metal cross-sectional area vs. deposited metal weight data obtained in experiments in which the weight of metal deposited per unit time is changed over a broad range, a second conversion diagram for converting deposited metal weight to workpiece deposited metal cross-sectional area can be generated (FIGS. 8 and 9). The difference between the molten metal and deposited metal cross-sectional areas, as obtained from these two conversion diagrams, is the effective cross-sectional area.
However, because effective heat input and deposited metal weight tend to vary within a narrow range during the welding time, results of computations based on instantaneous values of these variables may not always match reference standard values for good weld quality. However, when values of effective heat input and deposited metal weight, as well as values of the parameters that are computed based on them (molten metal cross-sectional area, deposited metal cross-sectional area, and effective cross-sectional area) are computed as averages of those values over the welding time, the values conform to actual conditions, and provide realistic results.